Creating and Running .ts Files

Write your TypeScript code in a text editor and save the file with a .ts extension. Save the file using the UTF-8 character encoding.

function greet(name: string): string {
    return "Hello, " + name + "!";
}

const message: string = greet("TypeScript");
console.log(message);

TypeScript is a language that adds type information to JavaScript. You can specify types for variables, function parameters, and return values. TypeScript files cannot be run as-is; they must first be converted to JavaScript.

npx tsc hello.ts
node hello.js
Hello, TypeScript!

You can write comments (notes) in a .ts file. Comments are ignored by the compiler, so they are useful for leaving descriptions or notes about the code.

function greet(name: string): string {
    return "Hello, " + name + "!";
}

/*
  Generates a message and
  outputs it to the console.
*/
const message: string = greet("TypeScript");
console.log(message);

Running the above produces the following output:

npx tsc sample_comments.ts
node sample_comments.js
Hello, TypeScript!

TypeScript cannot be run as-is. Two steps are required: first convert it to a JavaScript file with the tsc command, then run it with Node.js.

Step 1: Compile the .ts file to a .js file

Use the npx tsc command to convert the TypeScript file to a JavaScript file.

npx tsc hello.ts

When compilation succeeds, hello.js is generated in the same directory.

Step 2: Run the generated .js file with Node.js

node hello.js
Hello, TypeScript!

Run directly with ts-node

Using ts-node, you can combine compilation and execution into a single step. It is convenient for checking behavior during development.

npx ts-node hello.ts
Hello, TypeScript!

Comparison of run methods

A .ts file is simply a plain text file. You can create one by writing TypeScript code in a text editor and saving it with a .ts extension.

Because TypeScript cannot be run directly, a conversion step to JavaScript is required. The basic flow is to compile with npx tsc and run the generated .js file with Node.js. For quick checks during development, using npx ts-node is convenient as it runs with a single command.

There are two types of comments: single-line comments (//) and multi-line comments (/* */). Single-line comments are used most often in day-to-day coding.

For recommended editors and environment setup, see Setup.